Zenimax allows addons but to not support them. In short, use them, Zenimax will not care if you do, however, they are not responsible for them in any way,
TES has always been about modding. I think thats the main reason its here.
Sadly, I think 2 addons are the main reasons why several, now high level players think this game is boring.
The skyshard/lorebook location addon/map and the guide to best exp/quest addon.
Sure, you dont "loose" time by looking for them, or dont get all the skyshards, and you get the best exp/hour.
But this way, you miss much about whats fun in the game. And also, I have heard several times that quests are boring, all the the same all the time.
Eh....I run around turning over every rock I see, any glimmer of blue light can be a skyshard but 99% its just the sky.
There are to many quests to mention, but Ive done one where there was several options and I choose to not kill the giant leader, which led to all giants in eastmarch didnt attack me. However, when I tried to get a quest from the fighters guild, who where the ones who wanted me to kill the giants.....they didnt give me one.
Another was a quite long quest, that I dont recall where it started, but the end was some kind of challenge to take out 3 different ghost of the same "sleeping" king. And each time I could choose one of 3 companions to come with me and assist. With 3 different skillsets.
And....in the end, I got a skillpoint! There been a lot of quests I find out in nowhere, who gives a skillpoint. I wonder if these are included in the fastest exp/lvl.
I am only level 41, so yes, if I used the addons, I would have all skyshards and be veteran level. But why? I dont want to miss the game. I want to play it!
And btw....I got an achievement today that I had found all the lorebooks in eastmarch! Hah! All by myself!